A variety of approaches to information recording and playback exist in the prior art. Electromechanical processes are commonly used in the audio industry for recording groove modulations representative of an audio signal in a lacquer master. One "passive" transducer system employs a phonograph stylus and an electromechanical transducer device to derive signal recorded on a record medium surface (e.g., disc).
Recently, it has been demonstrated that video disc-type records can be played back by a piezoelectric pressure sensor. This type of system, which is essentially an extrapolation of audio record systems, provides fairly good performance, at least when the needle and the record are clean and new.
A cutterhead for electromechanically recording a video signal in a metal master is described in U.S. Pat. No. 3,865,997 issued to J. B. Halter on Feb. 11, 1975 entitled, "TRIANGULAR PIEZOELECTRIC TRANSDUCER FOR RECORDING VIDEO INFORMATION". In that patent the cutting stylus employed for recording groove modulations in the master is modulated in accordance with the video information which is to be recorded.
These "passive" transducer systems have been successful despite a number of problems. For instance, piezoelectric recording transducers may have resonance problems which add cost and compromise performance. One shortcoming of the phonograph transducer is that it is often operated at close to its practical limit in terms of its ability to record high frequency information signals.
These and other shortcomings may be overcome by using an "active" transducer system. In an active playback system energy is focused on a target, for example an information bit positioned on a recording surface, and the reflected energy carries back the recorded signal information, somewhat analogous to radar. One type of "active" transducer system which is utilized for video recording and playback is the optical video disc system as described in U.S. Pat. No. 4,097,895, issued to Fred W. Spong on June 27, 1978, entitled "MULTILAYER OPTICAL RECORD". This system performs well, but like other optical systems, tends to be complicated because of the laser and associated precision optics and, moreover, energy path losses tend to be high.